Yes, I heard it is normal when they work an area and have to move pairs around during upgrades that they may place bridge taps on the lines which increase the line length. Once they complete their work they go back and remove the bridge taps so the lines return to their original state. How long that lasts, I don't know.
Now with a line that is Marginal to start with, you do need to test at the NID (to get outside DSL Stats to compare with DSL Stats from inside) to make sure you don't have something interfering with the inside wiring since it is extra sensitive being on the borderline to begin with. What would not affect a good line could drop your line in half or more easily and there are many things that are taken for granted that can do that (a huge list).
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EarthLink DSL FAQ »
How do I test at my NID? What does it look like?Regards,
Doctor Olds